That depends on a few of things:
1. What is your ISP speed? If you are running a 3 - 6 Mbps dsl line, or slower cable speeds, then 11g still has more than enough overhead...however, if you are running a 30 Mbps connection, yes, 11n would be desireable. (11g may be rated to 54 Mbps, but really, 22 - 24 Mbps is its practical limit)
2. What kind of wifi adapters are your devices running? If they are a mix of 11g/11n, then unless you run them on separate bands (with a dual-band router), they will still access at 11g speed.
3. Another thing to consider: Do you run a NAS, share music/video files etc. within your network? If you do, you still may want to make the move to 11n regardless of your internet speed, to maximize the movement of data within your network.
Personally, at this stage, I would recommend that if you do go to an 11n router, it makes sense to get a dual band router, and make sure it has gigabit ports.
Also keep in mind that if you prefer running 3d party firmware such as DDWRT, or Tomato, you will want to check and see if the router you are interested in is supported by your preferred firmware.
Deeds, not words